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| 1 | +/* | |
| 2 | + * Copyright (c) 2005, 2009, Oracle and/or its affiliates. All rights reserved. | |
| 3 | + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 4 | + * | |
| 5 | + * This code is free software; you can redistribute it and/or modify it | |
| 6 | + * under the terms of the GNU General Public License version 2 only, as | |
| 7 | + * published by the Free Software Foundation. Oracle designates this | |
| 8 | + * particular file as subject to the "Classpath" exception as provided | |
| 9 | + * by Oracle in the LICENSE file that accompanied this code. | |
| 10 | + * | |
| 11 | + * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 12 | + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 13 | + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 14 | + * version 2 for more details (a copy is included in the LICENSE file that | |
| 15 | + * accompanied this code). | |
| 16 | + * | |
| 17 | + * You should have received a copy of the GNU General Public License version | |
| 18 | + * 2 along with this work; if not, write to the Free Software Foundation, | |
| 19 | + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 20 | + * | |
| 21 | + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 22 | + * or visit www.oracle.com if you need additional information or have any | |
| 23 | + * questions. | |
| 24 | + */ | |
| 25 | + | |
| 26 | +package sun.nio.ch; | |
| 27 | + | |
| 28 | +import java.nio.channels.*; | |
| 29 | +import java.util.*; | |
| 30 | +import java.util.concurrent.ConcurrentHashMap; | |
| 31 | +import java.lang.ref.*; | |
| 32 | +import java.io.FileDescriptor; | |
| 33 | +import java.io.IOException; | |
| 34 | + | |
| 35 | +abstract class FileLockTable { | |
| 36 | + protected FileLockTable() { | |
| 37 | + } | |
| 38 | + | |
| 39 | + /** | |
| 40 | + * Creates and returns a file lock table for a channel that is connected to | |
| 41 | + * the a system-wide map of all file locks for the Java virtual machine. | |
| 42 | + */ | |
| 43 | + public static FileLockTable newSharedFileLockTable(Channel channel, | |
| 44 | + FileDescriptor fd) | |
| 45 | + throws IOException | |
| 46 | + { | |
| 47 | + return new SharedFileLockTable(channel, fd); | |
| 48 | + } | |
| 49 | + | |
| 50 | + /** | |
| 51 | + * Adds a file lock to the table. | |
| 52 | + * | |
| 53 | + * @throws OverlappingFileLockException if the file lock overlaps | |
| 54 | + * with an existing file lock in the table | |
| 55 | + */ | |
| 56 | + public abstract void add(FileLock fl) throws OverlappingFileLockException; | |
| 57 | + | |
| 58 | + /** | |
| 59 | + * Remove an existing file lock from the table. | |
| 60 | + */ | |
| 61 | + public abstract void remove(FileLock fl); | |
| 62 | + | |
| 63 | + /** | |
| 64 | + * Removes all file locks from the table. | |
| 65 | + * | |
| 66 | + * @return The list of file locks removed | |
| 67 | + */ | |
| 68 | + public abstract List<FileLock> removeAll(); | |
| 69 | + | |
| 70 | + /** | |
| 71 | + * Replaces an existing file lock in the table. | |
| 72 | + */ | |
| 73 | + public abstract void replace(FileLock fl1, FileLock fl2); | |
| 74 | +} | |
| 75 | + | |
| 76 | + | |
| 77 | +/** | |
| 78 | + * A file lock table that is over a system-wide map of all file locks. | |
| 79 | + */ | |
| 80 | +class SharedFileLockTable extends FileLockTable { | |
| 81 | + | |
| 82 | + /** | |
| 83 | + * A weak reference to a FileLock. | |
| 84 | + * <p> | |
| 85 | + * SharedFileLockTable uses a list of file lock references to avoid keeping the | |
| 86 | + * FileLock (and FileChannel) alive. | |
| 87 | + */ | |
| 88 | + private static class FileLockReference extends WeakReference<FileLock> { | |
| 89 | + private FileKey fileKey; | |
| 90 | + | |
| 91 | + FileLockReference(FileLock referent, | |
| 92 | + ReferenceQueue<FileLock> queue, | |
| 93 | + FileKey key) { | |
| 94 | + super(referent, queue); | |
| 95 | + this.fileKey = key; | |
| 96 | + } | |
| 97 | + | |
| 98 | + FileKey fileKey() { | |
| 99 | + return fileKey; | |
| 100 | + } | |
| 101 | + } | |
| 102 | + | |
| 103 | + // The system-wide map is a ConcurrentHashMap that is keyed on the FileKey. | |
| 104 | + // The map value is a list of file locks represented by FileLockReferences. | |
| 105 | + // All access to the list must be synchronized on the list. | |
| 106 | + private static ConcurrentHashMap<FileKey, List<FileLockReference>> lockMap = | |
| 107 | + new ConcurrentHashMap<FileKey, List<FileLockReference>>(); | |
| 108 | + | |
| 109 | + // reference queue for cleared refs | |
| 110 | + private static ReferenceQueue<FileLock> queue = new ReferenceQueue<FileLock>(); | |
| 111 | + | |
| 112 | + // The connection to which this table is connected | |
| 113 | + private final Channel channel; | |
| 114 | + | |
| 115 | + // File key for the file that this channel is connected to | |
| 116 | + private final FileKey fileKey; | |
| 117 | + | |
| 118 | + SharedFileLockTable(Channel channel, FileDescriptor fd) throws IOException { | |
| 119 | + this.channel = channel; | |
| 120 | + this.fileKey = FileKey.create(fd); | |
| 121 | + } | |
| 122 | + | |
| 123 | + @Override | |
| 124 | + public void add(FileLock fl) throws OverlappingFileLockException { | |
| 125 | + List<FileLockReference> list = lockMap.get(fileKey); | |
| 126 | + | |
| 127 | + for (;;) { | |
| 128 | + | |
| 129 | + // The key isn't in the map so we try to create it atomically | |
| 130 | + if (list == null) { | |
| 131 | + list = new ArrayList<FileLockReference>(2); | |
| 132 | + List<FileLockReference> prev; | |
| 133 | + synchronized (list) { | |
| 134 | + prev = lockMap.putIfAbsent(fileKey, list); | |
| 135 | + if (prev == null) { | |
| 136 | + // we successfully created the key so we add the file lock | |
| 137 | + list.add(new FileLockReference(fl, queue, fileKey)); | |
| 138 | + break; | |
| 139 | + } | |
| 140 | + } | |
| 141 | + // someone else got there first | |
| 142 | + list = prev; | |
| 143 | + } | |
| 144 | + | |
| 145 | + // There is already a key. It is possible that some other thread | |
| 146 | + // is removing it so we re-fetch the value from the map. If it | |
| 147 | + // hasn't changed then we check the list for overlapping locks | |
| 148 | + // and add the new lock to the list. | |
| 149 | + synchronized (list) { | |
| 150 | + List<FileLockReference> current = lockMap.get(fileKey); | |
| 151 | + if (list == current) { | |
| 152 | + checkList(list, fl.position(), fl.size()); | |
| 153 | + list.add(new FileLockReference(fl, queue, fileKey)); | |
| 154 | + break; | |
| 155 | + } | |
| 156 | + list = current; | |
| 157 | + } | |
| 158 | + | |
| 159 | + } | |
| 160 | + | |
| 161 | + // process any stale entries pending in the reference queue | |
| 162 | + removeStaleEntries(); | |
| 163 | + } | |
| 164 | + | |
| 165 | + private void removeKeyIfEmpty(FileKey fk, List<FileLockReference> list) { | |
| 166 | + assert Thread.holdsLock(list); | |
| 167 | + assert lockMap.get(fk) == list; | |
| 168 | + if (list.isEmpty()) { | |
| 169 | + lockMap.remove(fk); | |
| 170 | + } | |
| 171 | + } | |
| 172 | + | |
| 173 | + @Override | |
| 174 | + public void remove(FileLock fl) { | |
| 175 | + assert fl != null; | |
| 176 | + | |
| 177 | + // the lock must exist so the list of locks must be present | |
| 178 | + List<FileLockReference> list = lockMap.get(fileKey); | |
| 179 | + if (list == null) return; | |
| 180 | + | |
| 181 | + synchronized (list) { | |
| 182 | + int index = 0; | |
| 183 | + while (index < list.size()) { | |
| 184 | + FileLockReference ref = list.get(index); | |
| 185 | + FileLock lock = ref.get(); | |
| 186 | + if (lock == fl) { | |
| 187 | + assert (lock != null) && (lock.acquiredBy() == channel); | |
| 188 | + ref.clear(); | |
| 189 | + list.remove(index); | |
| 190 | + break; | |
| 191 | + } | |
| 192 | + index++; | |
| 193 | + } | |
| 194 | + } | |
| 195 | + } | |
| 196 | + | |
| 197 | + @Override | |
| 198 | + public List<FileLock> removeAll() { | |
| 199 | + List<FileLock> result = new ArrayList<FileLock>(); | |
| 200 | + List<FileLockReference> list = lockMap.get(fileKey); | |
| 201 | + if (list != null) { | |
| 202 | + synchronized (list) { | |
| 203 | + int index = 0; | |
| 204 | + while (index < list.size()) { | |
| 205 | + FileLockReference ref = list.get(index); | |
| 206 | + FileLock lock = ref.get(); | |
| 207 | + | |
| 208 | + // remove locks obtained by this channel | |
| 209 | + if (lock != null && lock.acquiredBy() == channel) { | |
| 210 | + // remove the lock from the list | |
| 211 | + ref.clear(); | |
| 212 | + list.remove(index); | |
| 213 | + | |
| 214 | + // add to result | |
| 215 | + result.add(lock); | |
| 216 | + } else { | |
| 217 | + index++; | |
| 218 | + } | |
| 219 | + } | |
| 220 | + | |
| 221 | + // once the lock list is empty we remove it from the map | |
| 222 | + removeKeyIfEmpty(fileKey, list); | |
| 223 | + } | |
| 224 | + } | |
| 225 | + return result; | |
| 226 | + } | |
| 227 | + | |
| 228 | + @Override | |
| 229 | + public void replace(FileLock fromLock, FileLock toLock) { | |
| 230 | + // the lock must exist so there must be a list | |
| 231 | + List<FileLockReference> list = lockMap.get(fileKey); | |
| 232 | + assert list != null; | |
| 233 | + | |
| 234 | + synchronized (list) { | |
| 235 | + for (int index=0; index<list.size(); index++) { | |
| 236 | + FileLockReference ref = list.get(index); | |
| 237 | + FileLock lock = ref.get(); | |
| 238 | + if (lock == fromLock) { | |
| 239 | + ref.clear(); | |
| 240 | + list.set(index, new FileLockReference(toLock, queue, fileKey)); | |
| 241 | + break; | |
| 242 | + } | |
| 243 | + } | |
| 244 | + } | |
| 245 | + } | |
| 246 | + | |
| 247 | + // Check for overlapping file locks | |
| 248 | + private void checkList(List<FileLockReference> list, long position, long size) | |
| 249 | + throws OverlappingFileLockException | |
| 250 | + { | |
| 251 | + assert Thread.holdsLock(list); | |
| 252 | + for (FileLockReference ref: list) { | |
| 253 | + FileLock fl = ref.get(); | |
| 254 | + if (fl != null && fl.overlaps(position, size)) | |
| 255 | + throw new OverlappingFileLockException(); | |
| 256 | + } | |
| 257 | + } | |
| 258 | + | |
| 259 | + // Process the reference queue | |
| 260 | + private void removeStaleEntries() { | |
| 261 | + FileLockReference ref; | |
| 262 | + while ((ref = (FileLockReference)queue.poll()) != null) { | |
| 263 | + FileKey fk = ref.fileKey(); | |
| 264 | + List<FileLockReference> list = lockMap.get(fk); | |
| 265 | + if (list != null) { | |
| 266 | + synchronized (list) { | |
| 267 | + list.remove(ref); | |
| 268 | + removeKeyIfEmpty(fk, list); | |
| 269 | + } | |
| 270 | + } | |
| 271 | + } | |
| 272 | + } | |
| 273 | +} | |